Controlling forward and reverse link traffic channel power

ABSTRACT

Forward link transmission power to a user terminal in a wireless communications system having a plurality of beams is controlled by determining a baseline power level, P baseline , from a received active pilot channel signal-to-noise ratio (SNR); determining a power margin, P margin , from an identified interference susceptibility; determining a power level correction, P correction , based on an identified quality of service metric (QSM); determining a fade correction factor, P fade , based on a detected fade environment; and setting P transmit  based on P baseline , P margin , P correction  and P fade . For example, P transmit  may be set to a power level that is substantially equal to the sum of P baseline , P margin , P correction  and P fade . The determination of each of P baseline , P margin , P correction  and P fade  may be performed in independently running control loops or processes.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Continuation in Part and claimspriority to U.S. patent application Ser. No. 11/781,883 filed Jul. 23,2007, entitled “Controlling Forward Link Traffic Channel Power”, whichis a continuation of U.S. patent application Ser. No. 10/267,289, filedOct. 8, 2002, entitled “Controlling Forward Link Traffic Channel Power”;now allowed, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

BACKGROUND

1. Field

The present aspects of the present invention generally relate towireless communications networks, and more particularly to methods andapparatus for controlling transmission power of both the forward andreverse links.

2. Background

There are a variety of wireless communication systems having multiplebeam or sector communication links. A satellite-based communicationsystem is one such example. Another example is a cellular communicationsystem.

A satellite-based communication system includes one or more satellitesto relay communications signals between gateways and user terminals.Gateways provide communication links for connecting a user terminal toother user terminals or users of other communications systems, such as apublic switched telephone network (PSTN). User terminals can be fixed ormobile, such as a mobile telephone, and positioned near a gateway orremotely located.

A satellite can receive signals from and transmit signals to a userterminal provided the user terminal is within the “footprint” of thesatellite. The footprint of a satellite is the geographic region on thesurface of the earth covered by the satellite communications system. Insome satellite systems, a satellite's footprint is geographicallydivided into “beams,” through the use of beam forming antennas. Eachbeam covers a particular geographic region within a satellite'sfootprint.

Some satellite communications systems employ code division multipleaccess (CDMA) spread-spectrum signals, as disclosed in U.S. Pat. No.4,901,307, issued Feb. 13, 1990, entitled “Spread Spectrum MultipleAccess Communication System Using Satellite or Terrestrial Repeaters,”and U.S. Pat. No. 5,691,174, which issued Nov. 25, 1997, entitled“Method and Apparatus for Using Full Spectrum Transmitted Power in aSpread Spectrum Communication System for Tracking Individual RecipientPhase Time and Energy,” both of which are assigned to the assignee ofthe present invention, and are incorporated herein by reference.

The method for providing CDMA mobile communications was standardized inthe United States by the Telecommunications Industry Association inTIA/EIA/IS-95-A entitled “Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System,”referred to herein as IS-95. Combined AMPS & CDMA systems are describedin TIA/EIA Standard IS-98. Other communications systems are described inthe IMT-2000UM, or International Mobile Telecommunications System2000/Universal Mobile Telecommunications System, standards covering whatare referred to as wideband CDMA (WCDMA), cdma2000 (such as cdma2000 1×or 3× standards, for example) or TD-SCDMA.

Cellular communications may also employ CDMA techniques. However,instead of receiving signals from gateways that are relayed through oneor more satellites, user terminals receive signals from a fixed positionbase station that supports multiple sectors, each corresponding to aparticular geographic region, similar to having multiple beams.

Gateways and base stations transmit information in the form of wirelesssignals to user terminals across forward link communications channels.These wireless signals need to be transmitted at power levels sufficientto overcome noise and interference so that the transfer of informationoccurs within specified error rates. In addition, these wireless signalsneed to be transmitted at power levels that are not excessive so thatthey do not interfere with communications involving other userterminals. Faced with this challenge, gateways and base stations employdynamic forward link power control techniques to establish appropriateforward link transmit power levels.

Conventional forward and reverse link power control techniques involveclosed loop approaches where user terminals provide gateways and basestations with feedback that specifies particular transmit poweradjustments. For example, one such approach involves a user terminaldetermining signal-to-noise ratios (SNRs) of received forward linktraffic signals. Based on these determined SNRs, the user terminaltransmits commands that direct the gateway or base station to eitherincrease or decrease the transmit power of traffic signals sent to theuser terminal.

These commands are referred to as up/down commands because they directeither a power increase or a power decrease. Up/down commands aretransmitted to the gateway or base station across an up/down powercontrol channel. This channel is typically implemented by “puncturing”the up/down commands into frames of user terminal data that aretransmitted to the gateway or base station. This puncturing can limitthe data rates at which user terminals transmit information to gatewaysand base stations. Additionally, punctured channels may not be asreliable because punctured commands may introduce a higher bit errorrate for a given signal-to-noise ratio and punctured channels aresending uncoded bits reducing the reliability of the up/down commands.

In addition to transmitting up/down commands, user terminals typicallytransmit other types of information to gateways and base stations. Forexample, many user terminals periodically transmit various powermeasurements and noise measurements to support operations, such as“handoffs” between beams during an active call. To eliminate the lessreliable transmission of data rate limiting power adjustment commands,it is desirable for gateways and base stations to utilize suchtransmitted measurements to control forward link transmit power levels.

In addition, it is desirable to conserve forward link transmission powerto maximize capacity and minimize interference. It is desirable toconserve reverse link transmission power to minimize interference andconserve battery life. Since satellite and cellular communicationssystems employ multiple beams, transmissions received by user terminalsin a particular beam are susceptible to interference from transmissionsdesignated for neighboring beams. A user terminal's interferencesusceptibility is related to its proximity to adjacent beams. A userterminal's reverse link is also susceptible to other users transmittingin the same beam or sector (an orthogonal interferer). Namely, thecloser a user or user terminal is to an adjacent beam (a non-orthogonalinterferer), the more susceptible the user is to interference fromneighboring beams. Additionally, narrow band or wide band jammers mayexist in close proximity to the user, increasing their interferencesusceptibility.

In a satellite-based communications system where the satellites are notstationary, the geographic area covered by a given satellite isconstantly changing. As a result, a user terminal positioned within aparticular beam of a particular satellite at one point in time can laterbe positioned within a different beam of the same satellite and/orwithin a different beam of a different satellite. Furthermore, becausesatellite communication is wireless, a user terminal is free to moveabout. As a result, user terminals typically have varying positionswithin a beam while receiving transmissions across forward linkchannels. Accordingly, their susceptibility to interference may varyover time.

One technique for reducing interference received by user terminals is toboost the power of signals that are transmitted by satellites and/orcellular base stations to user terminals by a fixed margin. However,since user terminals can experience varying degrees of interferencesusceptibility, this approach has the drawback of wasting power on usersthat are not as susceptible to interference as others. In addition, thisapproach can cause additional interference with other user terminals.

Accordingly, as with the elimination of user terminals needing totransmit closed loop power adjustment commands, techniques for reducinginterference while conserving transmit power are desirable, especiallyin systems having limited power budgets.

SUMMARY

The aspects of the present invention are directed to apparatus andmethods for controlling forward or reverse link transmission power,P_(transmit), to or from a user terminal in a wireless communicationssystem. The systems and methods determine a baseline power level,P_(baseline), from a received active pilot channel signal-to-noise ratio(SNR); determine a power margin, P_(margin), from an identifiedinterference susceptibility; determine a power level correction,P_(correction), based on an identified Quality of Service Metric (QSM)such as packet error rate (PER), determine a fade attack power margin,P_(fade); and set P_(transmit) based on P_(baseline), P_(margin),P_(correction), and P_(fade). For example, P_(transmit) may be set to apower level that is substantially equal to the sum of P_(baseline),P_(margin), P_(correction), and P_(fade). For that matter, P_(transmit)may be any function of P_(baseline), P_(margin), P_(correction), andP_(fade). The determination of each of these components may be performedusing independently running control loops or processes.

Determining P_(baseline) may include calculating a power level offset,PO, and adding P_(o) to a pilot channel transmit power level.Identifying a user terminal interference susceptibility may includereceiving from the user terminal a plurality of signal powermeasurements.

Determining a power level correction, P_(correction), may includeidentifying a packet error rate (PER) associated with a user terminaldetermining P_(correction) may include increasing P_(correction) whenthe identified PER is greater than a desired PER, and decreasingP_(correction) when the identified PER is less than the desired PER.

Each of these signal power measurements corresponds to one of aplurality of beams. For example, these measurements may be pilot signalpower measurements conveyed in a pilot strength measurement message(PSMM). Alternatively, these measurements may be conveyed using othertypes of signals such as a paging message, or an interferencesusceptibility message. The differences between a first of the signalpower measurements, (such as one corresponding to the active beam, orthe strongest measurement) and each of the other signal powermeasurements are calculated.

P_(margin) is set to a first power level when the smallest of thecalculated differences is greater than a predetermined threshold.Alternatively, P_(margin) is set to a second power level when thesmallest of the calculated differences is less than or equal to thepredetermined threshold. This first power level is less than the secondpower level. Additionally, there may be N levels or thresholds thatdifferentiate the P_(margin) mapping.

P_(margin) may also be dependent on interference outside the currentcommunication system, otherwise known as jammers. The identification ofjammers may be based upon mobile assisted measurements of interferersand their associated bandwidths (narrow or wide band).

Determining P_(fade) may include calculating or detecting when thesignal is attenuated in a fade. This may be accomplished by monitoringthe signal to noise ratio (SNR) and comparing it to previous or filteredhistorical values, using commonly accepted filtering practices. When thepresence of a signal fade is identified, increasing P_(fade) will helpthe signal overcome the current fade.

Identifying a user terminal interference susceptibility mayalternatively include determining the location of the user terminalwithin one of the plurality of beams. In this case, P_(margin) is set toa first power level when the identified location is within a beamcrossover region. Otherwise, P_(margin) is set to a second power levelwhen the identified location is within a beam central region. Here, thefirst power level is greater than the second power level.

A system for controlling P_(transmit) includes a selector thatdetermines P_(baseline), P_(margin), P_(correction) and P_(fade). Atransceiver sets P_(transmit) based on P_(baseline), P_(margin),P_(correction), and P_(fade). For example, by setting P_(transmit) to apower level that is substantially equal to the sum or any other functionof P_(baseline), P_(margin), P_(correction), and P_(fade).

An advantage of the present invention is that it eliminates the need forclosed loop forward link power control techniques where user terminalstransmit up/down commands that specify particular forward or reverselink transmit power adjustments.

Another advantage of the present invention is that it keeps interferencelevels within acceptable ranges, while conserving transmit power.

Further features and advantages of the present invention, as well as thestructure and operation of various embodiments of the present invention,are described in detail below with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary wireless communication system;

FIG. 2 illustrates an exemplary footprint having a plurality of beams;

FIG. 3 illustrates an operational scenario within a satellite footprint;

FIG. 4 is a graph showing signal power as seen by the user terminal;

FIGS. 5-7 are flowcharts illustrating operational sequences of anembodiment;

FIG. 8 is a flow chart showing the operation of setting P_(margin);

FIG. 9 is a flow chart showing the operation of setting P_(fade);

FIG. 10 is a block diagram of an exemplary gateway implementation; and

FIG. 11 is a block diagram of a forward link transceiver implementation.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

I. Exemplary Operational Environment

Before describing aspects of the invention in detail, it is helpful todescribe an example environment in which the claimed invention may beimplemented. The presently claimed invention is particularly useful inmobile communications environments. FIG. 1 illustrates such anenvironment.

FIG. 1 is a block diagram of an exemplary wireless communication system(WCS) 100 that includes a base station 112, two satellites 116 a and 116b, and two associated gateways (also referred to herein as hubs) 120 aand 120 b. These elements engage in wireless communications with userterminals 124 a, 124 b, and 124 c. Typically, base stations andsatellites/gateways are components of distinct terrestrial and satellitebased communication systems. However, these distinct systems mayinteroperate as an overall communications infrastructure.

Although FIG. 1 illustrates a single base station 112, two satellites116, and two gateways 120, any number of these elements may be employedto achieve a desired communications capacity and geographic scope. Forexample, an exemplary implementation of WCS 100 includes 48 or moresatellites, traveling in eight different orbital planes in Low EarthOrbit (LEO) to service a large number of user terminals 124.

The terms base station and gateway are also sometimes usedinterchangeably, each being a fixed central communication station, withgateways, such as gateways 120, being perceived in the art as highlyspecialized base stations that direct communications through satelliterepeaters while base stations (also sometimes referred to ascell-sites), such as base station 112, use terrestrial antennas todirect communications within surrounding geographical regions. However,the claimed invention is not limited to multiple access communicationsystems, and may be employed in other types of systems that employ otheraccess techniques.

In this example, user terminals 124 each have or include apparatus or awireless communication device such as, but not limited to, a cellulartelephone, wireless handset, a data transceiver, or a paging or positiondetermination receiver. Furthermore each of user terminals 124 can behand-held, portable as in vehicle mounted (including cars, trucks,boats, trains, and planes) or fixed, as desired. For example, FIG. 1illustrates user terminal 124 a as a fixed telephone, user terminal 124b as a hand-held device, and user terminal 124 c as a vehicle-mounteddevice. Wireless communication devices are also sometimes referred to asuser terminals, mobile stations, mobile units, subscriber units, mobileradios or radiotelephones, wireless units, terminals, or simply as‘users’, subscribers, and ‘mobiles’ in some communication systems,depending on preference.

User terminals 124 engage in wireless communications with other elementsin WCS 100 using code division multiple access (CDMA) techniques.However, the presently claimed invention may be employed in systems thatemploy other communications techniques, such as time division multipleaccess (TDMA), and frequency division multiple access (FDMA), or otherwaveforms or techniques listed above (WCDMA, CDMA2000 . . . ).

Generally, beams from a beam source, such as base station 112 orsatellites 116, cover different geographical areas in predefinedpatterns. Beams at different frequencies, also referred to as CDMAchannels, frequency division multiplexed (FDM) signals or channels, or‘sub-beams’ can be directed to overlap the same region. It is alsoreadily understood by those skilled in the art that beam coverage orservice areas for multiple satellites, or antenna patterns for multiplebase stations, might be designed to overlap completely or partially in agiven region depending on the communication system design and the typeof service being offered, and whether space diversity is being achieved.

FIG. 1 illustrates several exemplary signal paths. For example, signalpaths 130 a-c provide for the exchange of signals between base station112 and user terminals 124. Similarly, signal paths 138 a-d provide forthe exchange of signals between satellites 116 and user terminals 124.Communications between satellites 116 and gateways 120 are facilitatedby signal paths 146 a-d.

User terminals 124 are capable of engaging in bi-directionalcommunications with base station 112 and/or satellites 116 acrossvarious channels. These channels can be traffic or data channels. Thesecommunications are carried across one or more forward link channels andone or more reverse link channels. These channels convey radio frequency(RF) signals across signal paths 130, 138, and 146.

Forward link channels transfer information to user terminals 124. Forexample, forward link traffic channels convey signals carryinginformation, such as digitally encoded voice and data. To receive andprocess this information, a user terminal 124 needs to acquire theforward link traffic channel timing. This timing acquisition isperformed through the reception of a corresponding forward link pilotchannel that conveys a pilot signal.

FIG. 1 illustrates several exemplary forward and reverse link channels.A forward link traffic channel conveys information signals from basestation 112 to user terminal 124 a. User terminal 124 a acquires thetiming of forward link traffic channel through the reception of pilotsignals by base station 112 on a forward link pilot channel. Bothtraffic channel and pilot channel signals are transferred over signalpath 130 a (not shown). Similarly, a reverse link traffic channelconveys information signals from user terminal 124 a to base station 112over signal path 130 a (not shown).

Within the context of satellite-based communications involving userterminal 124 c, satellite 116 a, and gateway 120 a, a forward linktraffic channel, a forward link pilot channel, and a reverse linktraffic channel transfer signals over signal paths 146 a and 138 c (notshown). Thus, terrestrial-based links typically involve a singlewireless signal path between the user terminal and base station, whilesatellite-based links typically involve two, or more, wireless signalpaths between the user terminal and a gateway through at least onesatellite (ignoring multipath).

As described above, WCS 100 performs wireless communications accordingto CDMA techniques. Thus, signals transmitted across the forward andreverse links of signal paths 130, 138, and 146 convey signals that areencoded, spread, and channelized according to CDMA transmissionstandards. In addition, block interleaving may be employed across theseforward and reverse links. These blocks are transmitted in frames (alsoreferred to herein as packets) having a predetermined duration, such as20 milliseconds.

Base station 112, satellites 116, and gateways 120 may adjust the powerof the signals that they transmit across the forward link trafficchannels of WCS 100. This power (referred to herein as forward trafficchannel transmit power) may be varied according to commands, requests,or feedback from user terminal 124, or according to time. This timevarying feature may be employed on a periodic basis. For example, thisfeature may be employed on a frame-by-frame basis. Alternatively, thisfeature may be employed on other time boundaries that are either largeror smaller than a frame. Such power adjustments are performed tomaintain forward link bit error rates (BER) and/or packet error rates(PER) within specific requirements, reduce interference, and conservetransmission power.

For example, gateway 120 a, through satellite 116 a, may transmitforward link traffic channel signals to user terminal 124 b at adifferent transmit power than it does for user terminal 124 c.Additionally, gateway 120 a may vary the forward traffic channeltransmit power of each of the forward links to user terminals 124 b and124 c for each successive frame.

As described above, pilot signals provide timing and phase referencesfor corresponding traffic signals. These timing references include aphase reference of codes that enables user terminals 124 to becomesynchronized with the spreading and channelizing functions performed bygateways 124 and base station 112. In addition, this phase referenceallows user terminals 124 to coherently demodulate received trafficsignals.

WCS 100 may feature different communications offerings across theseforward links, such as low data rate (LDR) and high data rate (HDR)services. An exemplary LDR service provides forward links having datarates from 3 kilobits per second (kbps) to 9.6 kbps, while an exemplaryHDR service supports typical data rates as high as 604 kbps or more.

HDR service may be bursty in nature. That is, traffic transferred acrossHDR links may suddenly begin and end in an unpredictable fashion. Thus,in one instant, an HDR link may be operating at zero kbps, and in thenext moment operating at a very high data rate, such as 604 kbps.

FIG. 2 illustrates an exemplary satellite beam pattern 202, also knownas a footprint. As shown in FIG. 2, the exemplary satellite footprint202 includes sixteen beams 204 ₁-204 ₁₆. Each beam covers a specificgeographical area, although there usually is some beam overlap. Thesatellite footprint shown in FIG. 2 includes an inner beam (beam 204 ₁),middle beams (beams 204 ₂-204 ₇), and outer beams (beams 204 ₈-204 ₁₆).Beam pattern 202 is a configuration of particular predefined gainpatterns that are each associated with a particular beam 204.

Beams 204 are illustrated as having non-overlapping geometric shapes forpurposes of illustration only. In fact, beams 204 each have gain patterncontours that extend well beyond the idealized boundaries shown in FIG.2. However, these gain patterns are attenuated beyond these illustratedboundaries such that they do not typically provide significant gain tosupport communications with user terminals 124 outside of a given“boundary”.

Beams 204 may each be considered to have different regions based ontheir proximity to one or more other beams and/or position within otherbeam gain patterns. For example, FIG. 2 illustrates beam 204 ₂ having acentral region 206 and a crossover region 208. Crossover region 208includes portions of beam 204 ₂ that are in close proximity to beams 204₁, 204 ₃, 204 ₇, 204 ₈, 204 ₉, and 204 ₁₀. Because of this proximity,user terminals 124 within crossover region 208 (as well as similarregions in other beams) are more likely to handoff to an adjacent beam,than are user terminals 124 in central region 206. However, userterminals 124 within handoff probable regions, such as crossover region208, are also more likely to receive interference from communicationslinks in adjacent beams 204.

To illustrate this principle, FIG. 3 shows an exemplary operationalscenario within footprint 202. This operational scenario involves userterminals 124 d-f communicating through different beams of a satellite116. In particular, user terminals 124 d and 124 e are communicatingwith satellite 116 through beam 204 ₂, while user terminal 124 f iscommunicating with satellite 116 through beam 204 ₇. As shown in FIG. 3,user terminal 124 d is within central region 206 of beam 204 ₂ and userterminal 124 e is within crossover region 208 of beam 204 ₂.

As described above, crossover region 208 is closer to beam 204 ₇ than iscentral region 206. Because of this proximity, user terminal 124 ewithin crossover region 208 can be within a higher gain portion of thebeam 204 ₇ gain pattern than can user terminal 124 d within centralregion 206. For instance, in the operational scenario of FIG. 3, userterminal 124 f receives a forward link transmission 302 from satellite116. In addition, user terminals 124 d and 124 e receive thistransmission as attenuated transmissions 302′ and 302″. Although bothare weaker than transmission 302, transmission 302″ is stronger thantransmission 302′.

In addition to receiving these attenuated transmissions, user terminals124 d and 124 e also receive forward link transmissions from satellite116 that are intended for their reception. In particular, user terminal124 d receives a forward link transmission 304 from satellite 116 anduser terminal 124 e receives a forward link transmission 306 fromsatellite 116.

In the context of exemplary WCS 100, downlink CDMA transmissions withina particular beam 204 are orthogonally encoded. That is, they are notgenerally interfering with each other. However, downlink CDMAtransmissions from different beams are not necessarily orthogonal, andmay interfere with each other. Thus, in the operational scenario of FIG.3, the reception of transmission 304 is susceptible to interference fromtransmission 302′. Similarly, the reception of transmission 306 issusceptible to interference from transmission 302″. Furthermore, thereception of 304 is susceptible to interference from jammer 305.

FIG. 4 graphically shows the signal power as seen by user terminal 124D.Power is in the first axis and frequency is shown in the other. Userterminal 124D will have information regarding the forward linkinterference, measurements of orthogonal signals within the beam/sector308, measurements of non-orthogonal system interference 310 from usersoutside the current sector/beam, and it is possible for the userterminal to measure jammers within RF band of interest 312. For example,beam 204 ₇ can be an in-band source of interference and will bemeasurable by terminal 124D. Jammer 305 will also be a source ofinterference and terminal 124D may be able to measure the impact of thisjammer 305 as well. An adjacent communication system, may also be asource of interference 306 as shown in FIG. 4. User terminal 124D may ormay not be able to characterize this source of interference 306. Allthis information, collected by terminal 124D, may be accumulated into aforward link interference message that can be exchanged with the basestation for purposes of interference mitigation techniques or transmitpower control. As an example, the base station can reduce ‘other sector’traffic from sector 204 ₇, to reduce interference, based on theaggregate of measurements from user terminals. Additional knowledge ofinterference power from adjacent channel 306 and jammer 305 allows thebase station to take necessary mitigation techniques, which may involve,but are not limited to, increasing the power control set points,determining P_(margin) for user terminals impacted, or limiting themaximum expected throughput for users and only using more reliable lowerdata rate services in the presence of these interferers, thus preventinga poor quality of service that would be present with higher data rates.

Jammer 305 may potentially be located within the signal band ofinterests as indicated by the jammer labeled 305′, making its detectionmore difficult and its impact greater. The knowledge of whetherinterference is narrow band, jammer 305, or wide band adjacent channel306, will allow the base station to further optimize the requiredP_(margin) necessary for terminal 124D to have proper quality ofservice.

II. Power Control Architecture

Communications systems, such as WCS 100, specify certain maximum BERsand/or PERs for signals transmitted across their wireless communicationschannels as being useful for desired link quality of service (QoS). Themetrics used to measure QoS are often known as Quality of ServiceMetrics (QSM). For a channel to perform as intended, these error ratesmust not be exceeded, at least not for an appreciable amount of time. Achannel's error rates depend on a ratio of power levels that is referredto herein as a signal-to-noise ratio (SNR). This ratio is expressedbelow in Equation (1).

$\begin{matrix}\frac{E_{b}}{N_{t}} & (1)\end{matrix}$

In Equation (1), E_(b) represents the energy per transmitted bit andN_(t) represents a noise energy. N_(t) includes two components: N₀ andI_(t). N_(o) represents thermal noise and I_(t) represents interferencepower.

N_(o) is relatively constant in wireless communications environments,such as the environment of WCS 100. However, I_(t) can vary greatly.Since I_(t) can vary greatly, the ratio of Equation (1), as well as theassociated link error rates, can fluctuate across a large range ofvalues.

Error rates, such as BER and PER, are functions of SNR. Namely, as SNRincreases, these error rates decrease. Therefore, increasing E_(b) byboosting the power of signals transmitted across a forward link channelis one way to keep error rates beneath specified maximum levels.Unfortunately, wireless communications systems, such as WCS 100, includecomponents, such as satellites 116, which have limited availabletransmit power. The present aspect efficiently allocates this availablepower to multiple traffic channels.

This provides a power control architecture that efficiently allocatestransmit power to communications channels, such as forward link trafficchannels. FIG. 5 is a flowchart illustrating an operation according tothis architecture. This operation is described in the context of forwardlink traffic channel communications from gateway 120 a to user terminal124 a. However, this operation may be applied to communications betweena variety of user terminals 124 and gateways 120 or base stations 112.

As described above, conventional techniques for forward link powercontrol involve closed loop approaches where user terminals providegateways or base stations with commands, such as up/down commands, thatspecify particular forward link traffic channel power adjustments. Suchcommands are typically transmitted across a reverse link up/down commandchannel. The power control architecture of FIG. 5 advantageouslyeliminates the need for such channels.

In a step 402, gateway 120 a performs a noise based power control. Asshown in FIG. 5, step 402 includes steps 408 and 410. In step 408,gateway 120 a receives an active pilot channel SNR measurement from auser terminal 124 a. Gateway 120 a transmits pilot channel signals atconstant power. Therefore, this received SNR estimate provides a frameof reference for determining transmit power levels for forward linktraffic channels. Accordingly, from this received SNR, gateway 120 adetermines a baseline power level, P_(baseline), in step 410. Thisdetermination is described in greater detail below with reference toFIG. 5.

In a step 404, gateway 120 a performs an interference based powercontrol. Step 404 includes steps 412 and 414. In step 412, gateway 120 aidentifies a susceptibility of user terminal 124 a to interferingtransmissions that involve other user terminals 124. Although suchinterfering transmissions are difficult to predict and can havefluctuating levels, the operational environment of user terminal 124 adetermines the interference susceptibility of user terminal 124 a. Dueto the nature of these signals, commonly accepted filtering practicesmay be necessary to properly assess the average interference levels fortheir given purpose. The filtering operation, will help minimize thechanges to a time period that reduces overhead messaging and preventschanges that are based on a noisy measurement versus a real signaltrend. This determination is described in greater detail below withreference to FIG. 6.

The interference susceptibility of user terminal 124 a corresponds to arange of possible interference power levels. From this determinedinterference susceptibility, gateway 120 a determines a correspondingpower margin, P_(margin), in step 414.

In a step 406, gateway 120 a performs an error rate based power control.As shown in FIG. 5, step 406 includes steps 416 and 418. In step 416,gateway 120 a identifies a forward link Quality of Service Metric (QSM),such as a packet error rate (PER) to effectively measure the Quality ofService (QoS) of the user terminal. In step 418, gateway 120 adetermines a power level correction, P_(correction), from the identifiederror rate.

Step 422 is signal fade adjustment. In this step, gateway 120 aidentifies the fade 424 and calculates the fade correction 426.

In a step 420, gateway 120 a sends forward link traffic channeltransmissions to user 124 a having a transmit power, P_(transmit), thatis based on P_(baseline), P_(margin), and P_(correction) according to arelationship, such as the one expressed below in Equation (2), but itcould easily be any function or operation of these elements.

P _(transmit) =P _(baseline) +P _(margin) +P _(correction) +P_(fade)  (2)

As described above, a forward link traffic channel's error rates dependon its SNR. P_(baseline), P_(margin), P_(correction) and P_(fade) areeach determined in steps 402, 404, 406, and 422 to maintain forward linktraffic channel quality of service estimates (QSM), such as bit errorrate (BER) and packet error rate (PER), within specific requirements.The requirements may be selected as desired, and alternatively may bedynamically adjusted over time.

III. Noise Based Power Control

As described above with reference to FIG. 5, P_(baseline) is determinedby gateway 120 a in step 410. Gateway 120 a adjusts P_(baseline) sothat, in the absence of interference from other RF energy sources,forward link information error rates are maintained within specifiedrequirements. P_(baseline) is determined from SNR measurements taken byuser terminal 124 a that characterize the reception quality of activebeam pilot channel signals.

As shown in FIG. 1, gateway 120 a communicates with user terminal 124 athrough satellite 116 a. Satellite 116 a supports communications acrossa footprint that includes a plurality of beams, such as beams 204.Gateway 120 a transmits a plurality of forward link pilot channelsignals. Each of these pilot channel signals is relayed by satellite 116a in a respective one of the plurality of beams.

These pilot channel signals employ time-based offsets of a given PN codesequence. Furthermore, gateway 120 a transmits these pilot signals at asubstantially constant power.

User terminal 124 a is serviced by one of the plurality of beams ofsatellite 116 a. This beam is referred to herein as the active beam ofuser terminal 124 a. User terminal 124 a measures an active beam pilotsignal SNR and transmits the results of this measurement to gateway 120a. This transmitted measurement may be in the form of a message thatuser terminal 124 a periodically sends to gateway 120 a.

Since forward link pilot channel signals are transmitted at a constantpower, these SNR measurements transmitted by user terminal 124 a providegateway 120 a with a frame of reference for determining adequate forwardlink traffic channel transmit power levels in the absence ofinterference.

The active pilot channel SNR measurements received from user terminal124 a are each expressed herein as E_(cp)/N_(t), where E_(cp) representsthe energy per pilot signal chip. As described above, gateway 120 areceives E_(cp)/N_(t) in step 408. From E_(cp)/N_(t), gateway 120 adetermines a power level for P_(baseline). In the absence ofinterference, forward link traffic channel signals transmitted atP_(baseline) will be within specified error rate limits when received byuser terminal 124 a.

FIG. 6 is a flowchart illustrating a performance of step 410 in greaterdetail. This performance begins with a step 502, where gateway 120 acalculates a power level offset, P_(o), according to the relationship(3) below.

P _(o) =E _(bt) /N _(t)+10 log(R/W)−E _(cp) /N _(t)  (3)

In Equation (3), E_(bt)/N_(t) is a desired forward link traffic channelSNR in decibels (dB), R is the forward link traffic channel data rate, Wis the forward link traffic channel spreading bandwidth, E_(cp)/N_(t) isthe received active pilot channel SNR measurement in dB and R/W is theprocessing gain. E_(bt)/N_(t) is selected to achieve a desired BER forforward link traffic channel transmissions to user terminal 124 a.

A step 504 follows step 502. In step 504, gateway 124 a adds PO to thepower level used to transmit pilot channel signals to user terminal 124a. Next, in a step 506, gateway 120 a sets P_(baseline) to the result ofthe addition performed in step 504.

Two examples of these steps are now described in the context of Equation(3). For both of these examples, the desired forward link trafficchannel SNR (E_(b)t/N_(t)) is 1 dB. In the first example, R=6.048 kbpsand W=1.2288 MHz. If gateway 120 a receives from user terminal 124 a anE_(cp)/N_(t) value of −21 dB, then P_(o) is approximately −1 dB. Thus,in this example, gateway 120 a sets P_(baseline) at 1 dB less than thecorresponding pilot channel transmit power.

In the second example, R=9.6 kbps and W=1.2288 MHz. If gateway 120 areceives from user terminal 124 a an E_(cp)/N_(t) value of −21 dB, thenP_(o) is approximately 1 dB. Thus, in this example, gateway 120 a setsP_(baseline) at 1 dB greater than the corresponding pilot channeltransmit power. These two examples illustrate that, as data ratesincrease, so does the differential between pilot transmit power andtraffic transmit power.

IV. Interference Based Power Control

As described with reference to the operational scenario of FIG. 3, thesignal of interest, 206, is impacted through interference susceptibilityof signals, 302′, 302″, and 305. Accordingly, within the scenario ofFIG. 3, if the signal strength of 302″ is stronger than 302′, thereception of transmission 306 by user terminal 124 e is susceptible to agreater amount of interference than is the reception of transmission 304by user terminal 124 d. Gateway 120 a applies this principle in step 404to reduce such interference while conserving transmit power.

Forward link traffic channel signals that are directed to other userterminals 124 in different beams may interfere with traffic channelsignals directed to user terminal 124 a. As described above withreference to Equation (1), interference power levels (expressed asI_(t)) may vary greatly. Such variations cause the forward link trafficchannel SNR, as well as the associated error rates, to fluctuate over alarge range of values.

The reason for such fluctuations is described with reference to Equation(4), below. Equation (4) expresses the interference noise component,I_(t,i), that a user, i, receives from the forward link traffic channeltransmissions of a set of interfering users (indexed by the variable j).

$\begin{matrix}{I_{t,i} = {\sum\limits_{j \neq t}\; \frac{P_{j} \cdot R_{j}}{W}}} & (4)\end{matrix}$

In Equation (4), P_(j) is the forward link transmit power directed to auser, j, R_(j) is the data rate of the forward link power to user j, andW is the CDMA spreading bandwidth.

As expressed in Equation (4), the contribution of an interfering userterminal 124 to the forward link interference noise component of userterminal 124 a is directly proportional to the interfering userterminal's forward link data rate, R_(j). In accordance with therelationship of Equation (1), as forward link data rates increase, theinterference noise component, I_(t), of N_(t) becomes progressivelydominant over the corresponding thermal noise component, N₀.

As described herein with reference to FIG. 1, WCS 100 may offer both LDRand HDR services. Because of its substantially lower data rate,interference noise variations from LDR links are relatively small whencompared to interference noise variations from HDR links that transferbursty traffic at higher data rates. The base station or gateway willhave information regarding the user's data rates and sectors affected inthe forward link, this data may be used to evaluate the interference ofany given user in the system. Additionally, the user terminal will havemeasurements of forward link active sectors, adjacent sectors andjammers, enabling the gateway to properly compute P_(margin) for theforward link. In the reverse link, the gateway or base station will beable to determine the amount of traffic and the measured noise floor atthe receiver, thereby determining the interference levels that may thenbe fed back to the user terminal so it may adjust its P_(margin) for thereverse link transmit power.

To make sure that such interference variations do not compromisecommunications across or over wireless links, gateway 120 a includesP_(margin) as a forward link traffic channel transmit power component.P_(margin) mitigates interference from adjacent beam forward linktraffic channels.

As described above with reference to the operational scenario of FIG. 3,the location of a user terminal 124 within a beam affects itssusceptibility to interference. More specifically, a user terminal 124near the interface between two beams, such as a user terminal 124 incrossover region 208, is likely to receive more interference than a userterminal 124 further away from beam interfaces, such as a user terminal124 in central region 206. Therefore, to mitigate interference, gateway120 a may employ a smaller P_(margin) when user terminal 124 a is in acentral region than when user terminal 124 a is in a crossover region.Additionally, with today's location technology, the base station orgateway will have knowledge of the location within the sector or beam ofthe greatest sources of interference (other users). This knowledge mayaid in the determination of the required P_(margin). Location willprovide information regarding how disadvantaged the interferer's channelmay be and thus indicate the potential transmission power of thatinterfering signal. A signal on the edge of the beam or sector willpotentially interfere with more than one user terminal in the highestgeometry location, the center of the sector.

Accordingly, gateway 120 a determines P_(margin) based on the locationof user terminal 124 a within its active beam 204. As described abovewith reference to FIG. 5, P_(margin) is determined by gateway 120 instep 414. Accordingly, step 414 may comprise setting P_(margin) to afirst power level when the identified location is within a beamcrossover region, and setting P_(margin) to a second power level whenthe identified location is within a beam central region. Since userterminals 124 within beam crossover regions are more susceptible tointerference, the first power level in this example is greater than thesecond power level. FIG. 7 is a flowchart that illustrates a performanceof step 412 that implements this position-based feature. Thisperformance begins with a step 602, where gateway 120 a receives aplurality of signal power measurements from user terminal 124 a. Each ofthese power measurements corresponds to one of a plurality of beams. Forexample, each of these measurements may be pilot signal powermeasurements. These measurements may be in the form of a formattedmessage, such as a pilot strength measurement message (PSMM).

Next, in a step 604, gateway 120 a calculates the differences between afirst of the signal power measurements and each of the other signalpower measurements. This first power measurement may be of the activebeam pilot signal power or the largest power measurement. In this case,the smallest of these differences indicates the ability of user terminal124 a to receive forward link transmissions, such as interfering forwardlink traffic channel transmissions, from another beam. Accordingly, thesmallest of these differences indicates the interference susceptibilityof user terminal 124 a.

In a step 606, gateway 120 a determines whether the smallest of thedifferences calculated in step 604 is greater than a predeterminedthreshold. If so, then a step 608 is performed, where gateway 120 aconcludes that user terminal 124 a has a first interferencesusceptibility. Otherwise, a step 610 is performed, where gateway 120 aconcludes that user terminal 124 a has second interferencesusceptibility, which is greater than the first interferencesusceptibility.

The forward link interference susceptibility may be computed bydetermining the smallest difference as mentioned above, or it may be anyfunction of any or all the differences of interfering signal strengthswith the signal of interest. From this determination, values ofP_(margin) may be determined based on a single threshold mapping to twovalues of P_(margin), or N thresholds mapping to N+1 values forP_(margin), or P_(margin) may determined directly from a formula of thesusceptibilities. The calculation of P_(margin) will be greatlyfacilitated through the use of a message exchange with the userterminal, whereby the terminal communicates the levels of susceptibilityof orthogonal, non-orthogonal and jammer based interference. This addsthe additional benefit that the base station or gateway may then decideto reduce the interference levels by feeding back information to theoffending user terminals, which are interfering with the signal ofinterest, and throttling back the data traffic and hence theinterference for the user terminal of interest.

From this identified interference susceptibility, gateway 120 adetermines a corresponding P_(margin) value, as described above withreference to step 414 of FIG. 5. In particular, gateway 120 a determinesa P_(margin) according to a relationship where P_(margin) increases asthe interference susceptibility identified in step 412 increases.

For instance, as described above with reference to FIG. 7, gateway 120 adetermines the interference susceptibility of user terminal 124 a.Namely, gateway 120 a identifies a higher interference susceptibility instep 608 than in step 610. Thus, gateway 120 a sets P_(margin) to agreater value when step 414 follows step 608 than when step 414 followsstep 610.

Note that interference determination and calculation of P_(margin) maybe done by a gateway only mechanism, whereby the gateway notes the typeand power levels of data connections in adjacent beams/sectors, or itcan be a mobile assisted mechanism, whereby the user terminal sends amessage indicating the power levels of interfering signals which mayinclude orthogonal, non-orthogonal and jammer classifications of theinterference. The mobile assisted techniques will provide a more robustperformance than the gateway only approach. It is also possible for apower control mechanism to use a combination of both base station onlyand mobile assisted interference detection/mitigation.

In addition to directly controlling the P_(margin) of a given user, thebase station may use the interference estimates to institute aninterference mitigation policy by lowering data rates, endingconnections and lower power transmission levels to users that arecausing interference to the given user. FIG. 8 is a flow chart showingthe operation of setting P_(margin). From FIG. 8, the base stationreceives a message which includes multiple signal power and interferencemeasurements 1100, enabling a segregation of interference intoorthogonal noise, non-orthogonal noise or jammer noise 1110. The basestation or gateway may then choose which techniques to use 1120 whichmay be one or both techniques. The first technique, implementinginterference mitigation by lowering orthogonal or non-orthogonal sources1130 enables better user performance by lowering the interference in theother users 1140, such as lowering transmissions from 204 ₇ and 204 ₂users in FIGS. 4 and 3. Additionally, the gateway may decide to increasethe value of P_(margin) to boost the signal power by calculating adifference between the signal of interest and the interference signals1150, comparing the difference with N thresholds 1160 and mapping theappropriate threshold to the required P_(margin) value 1170. These stepswill be necessary in the presence of an uncontrollable noise source suchas 305 and 306 as seen in FIGS. 3 and 4.

V. Error Rate Based Power Control

As described above with reference to FIGS. 6 and 7, P_(baseline) andP_(margin) are determined in response to SNR and power measurements. Forinstance, gateway 120 a determines P_(baseline) in step 410 in responseto active pilot channel SNR measurements so that a desired forward linktraffic channel SNR (expressed in Equation (3) as Ebt/Nt) is achieved.This desired SNR corresponds to target error rate(s) based on arelationship that is determined by the modulation scheme and errorcorrection coding techniques employed by gateway 120 a in forward linktraffic channel transmissions.

Similarly, in step 414 gateway 120 a determines P_(margin) according toa comparison of pilot signal power measurements received from userterminal 124 a that identifies interference susceptibility. However,this identified interference susceptibility does not indicate actualinterference received by user terminal 124 a.

In contrast to P_(baseline) and P_(margin), P_(correction) is determinedby gateway 120 a in step 418 from actual link Quality of Service Metricthat user terminal 124 a encounters. As described above with referenceto FIG. 5, gateway 120 a identifies a forward link error rate, such asPER, in step 416.

Gateway 120 a sends information across the forward link traffic channelto user terminal 124 a in the form of packets. Each of these packets ismarked with a sequence identification number (sequence ID) that isassigned in a predetermined manner. User terminal 124 a monitors thesequence IDs of received packets and sends a message to gateway 120 awhen packets are received out of sequence.

This message, referred to herein as a negative acknowledgement (NAK)message, indicates a sequence ID that was missing in a series of packetsthat user terminal 124 a received from gateway 120 a. A missing sequenceID indicates a packet error. Gateway 120 a collects statistics on thenumber of NAK messages received from user terminal 124 a to compute theforward link traffic channel PER in step 416.

Accordingly, step 416 includes gateway 120 a counting the number ofnegative acknowledgement (NAK) messages received over a data collectioninterval. In addition, step 416 includes gateway 120 a calculating a PERaccording to a relationship, such as the one expressed below in Equation(5).

$\begin{matrix}{{PER} = \frac{NumberofreceivedNAKmessages}{Numberoftransmittedpackets}} & (5)\end{matrix}$

In Equation (5), gateway 120 a divides the number of NAK messagesreceived during the data collection interval by the number of packetsthat gateway 120 a transmitted during the data collection interval.

An alternative way to calculate a PER involves user terminal 124 areceiving packets containing cyclical redundancy check (CRC) bits. Foreach packet, user terminal 124 a uses these CRC bits to determinewhether the packet contains bit errors. If so, then user terminal 124 aincrements a packet error counter. User terminal 124 a may determine aPER by calculating the ratio of counted packet errors to receivederrors. This PER may periodically transmit such calculated PERs togateway 120 a. In addition, other known methods of calculating a PER, orother quality of service metrics, may be used within the embodimentswithout departing from the scope of the claimed invention.

As described above with reference to FIG. 5, gateway 120 a determines instep 418 a power level correction component, P_(correction), from theidentified error rate. Step 418 comprises comparing the PER identifiedin step 416 with a desired PER, and adjusting P_(correction)accordingly. In particular, this adjustment comprises gateway 120 aincreasing P_(correction) when the identified PER is greater than thedesired PER, and gateway 120 a decreasing P_(correction) when theidentified PER is less than the desired PER.

Additionally, the base station or gateway may associate a timer with aquality of service metric (PER for example) threshold, such that ifservice moves below a certain marginal level of performance for a givenamount of time, P_(correction) may be increased to ensure an acceptablelevel of performance. Furthermore, N levels of thresholds may be definedto map to N different correction factors, P_(correction).

VI. Fade Correction

For implementation on the reverse or forward link in a terrestrialcommunication system, the need exists to compensate for signal fadesthat happen relatively fast in the channel of interest. The termP_(fade) is computed to compensate for these fast fades on the forwardor reverse link. P_(fade) may be computed based on information fed backfrom the user terminal such as Eb/Nt measurements or any other SNRmetric, including filtered responses. This SNR is then used to computethe required P_(fade) to overcome the signal deficiency that may exist.

In the reverse link, the base station will use information from itsreceiver to gauge the fading that may exist and will then send a messageto the user terminal indicating what level of correction, P_(fade), isneeded to compensate for the fading environment or fade that is presentat the moment. FIG. 9 is a flow chart showing the steps to set P_(fade).Referring to FIG. 9, the gateway receives a periodic update of the SNRmetric 1000. The gateway then process a history of the SNR metrics todetermine if a fade is present 1010 and route the determination 1020. Ifno fade is detected 1030, the P_(fade) aspect may be ignored and thealgorithm may proceed 1040. If a fade is detected 1050, the gateway mustdetermine the magnitude of correction, P_(fade), necessary 1060 andadjust this value to set P_(fade) appropriately 1070.

VII. Timing

As shown in FIG. 5, steps 402, 404, and 406 may be performedsequentially. However, these steps may also be performed independentlyof each other. As described above, steps 402, 404, and 406 each involvereceiving information from user terminal 124 a. In response to thisinformation, these steps each set a corresponding transmit powercomponent.

As described above, noise based power control is performed in step 402.This power control involves gateway 120 a receiving SNR measurements,such as E_(cp)/N_(t), from user terminal 124 a, and in response settingP_(baseline). User terminal 124 a may periodically transmit these SNRmeasurements, such as once every second. Therefore, gateway 120 a mayperiodically set P_(baseline).

Interference based power control is performed in step 404. Changes ininterference susceptibility often change more slowly than changes in auser terminal's noise environment because interference based changes aredue to slower geometry changes that are caused by satellite motionand/or user terminal motion. Therefore, step 404 may involve gateway 120a receiving a set of pilot signal power measurements. These measurementsmay be in the form of a PSMM, which is also transmitted periodically,such as once every 10 seconds. Accordingly, gateway 120 a mayperiodically adjust P_(margin).

Gateway 120 a performs error rate based power control in step 406. Asdescribed above, this power control involves the receipt of NAK messagesover a data collection interval. This data collection interval may havevarious durations, as desired, as would be known. More reliable PERstatistics are gathered when longer data collection intervals areemployed. Therefore, gateway 120 a may periodically adjustP_(correction) once every data collection interval. An exemplary datacollection interval is 60 seconds.

VIII. Exemplary Gateway Implementation

FIG. 10 is a block diagram of an exemplary gateway 120 implementationthat performs the techniques described herein. Although described in thecontext of satellite communications, this exemplary implementation mayalso be employed in cellular base stations, such as base station 112 ofFIG. 1. As shown in FIG. 10, this implementation includes an antennasegment 702 that is coupled to a radio frequency (RF) subsystem 704, anda CDMA subsystem 706 that is coupled to RF subsystem 704. In addition,gateway 120 further includes a switch 708 that is coupled to CDMAsubsystem 706.

Antenna segment 702 includes one or more antennas that exchange RFsignals with one or more user terminals 124 through satellite(s) 116. Inparticular, antenna segment 702 receives reverse link RF signals andtransmits forward link RF signals. To enable the transmission andreception of RF signals through a single antenna, antenna segment 702may also include a diplexer (not shown).

RF subsystem 704 receives electrical signals from antenna segment 702within an RF frequency band. Upon reception, RF subsystem 704 downconverts these electrical signals from the RF frequency band to anintermediate frequency (IF). In addition, RF subsystem 704 may filterthe electrical signals received from antenna segment 702 in accordancewith a predetermined bandwidth.

To increase the power of the RF signals received from antenna segment702, RF subsystem 704 also includes amplification components (notshown). Exemplary amplification components include a low noise amplifier(LNA) that initially amplifies signals received from antenna segment702, and a variable gain amplifier (VGA) that further amplifies thesesignals after they are mixed down to IF during the aforementioned downconversion process.

As a result of these filtering, down conversion, and amplificationoperations, RF subsystem 204 produces an IF signal 720 that is sent to areverse link transceiver 712 within CDMA subsystem 706.

In addition to receiving reverse link RF signals from antenna segment702, RF subsystem 704 receives a forward link IF signal 722 from aforward link transceiver 710 within CDMA subsystem 706. RF subsystem 704amplifies and up converts this signal into a corresponding RF signal fortransmission by antenna segment 702.

As shown in FIG. 10, CDMA subsystem 706 includes a forward linktransceiver 710, a reverse link transceiver 712, a router 714, and aselector bank subsystem (SBS) 716. As described above, transceivers 710and 712 exchange IF signals 720 and 722 with RF subsystem 704. Inaddition, transceivers 710 and 712 perform CDMA operations.

In particular, forward link transceiver 710 receives one or more forwardlink information sequences 724 from router 714. Upon reception, forwardlink transceiver 710 converts these sequences into IF signal 722, whichis in a CDMA transmission format. This conversion is described ingreater detail below with reference to FIG. 11.

Reverse link transceiver 712 converts IF signal 720, which is in a CDMAtransmission format, into information sequences 726 a-726 n. Forexample, forward link transceiver 710 despreads and decovers IF signal720 with one or more PN sequences and channelizing codes. In addition,forward link transceiver 710 may perform decoding and de-interleavingoperations to produce information sequences 726, which are sent torouter 714.

Router 714 handles the transfer of information sequences 724 and 726,which may be in the form of packets, between SBS 716 and transceivers710 and 712. This transfer is performed across interface 728, which maybe a data network, such as a local area network (LAN), or any other wellknown mechanism for transferring information.

SBS 716 processes the forward link and reverse link traffic handled bygateway 120. This traffic includes both payload traffic and signalingtraffic. For example, SBS 716 exchanges signaling traffic in theperformance of call processing operations, such as call setup, callteardown, and beam hand-offs. SBS 716 also forwards traffic to switch708, which provides an interface to a public switched telephone network(PSTN).

SBS 716 includes a plurality of selectors 718 a-n for processing forwardand reverse link traffic. Each selector 718 handles activecommunications for a corresponding user terminal 124. However, selectors718 may be reassigned to other user terminals 124 upon the terminationof such active communications. For example, selectors 718 evaluatePSMMs, pilot signal SNR measurements, and NAK messages sent from userterminals 124 to perform appropriate forward link traffic channeltransmit power adjustments.

Each selector 718 may be implemented in a software-controlled processorprogrammed to perform the functions described herein. Suchimplementations may include well known standard elements or generalizedfunction or general purpose hardware including a variety of digitalsignal processors (DSPs), programmable electronic devices, or computersthat operate under the control of software instructions perform thedesired functions.

Each selector 718 controls forward link power control operations. Toadjust the power of forward link transmissions, selectors 718 each senda power control command 730 to forward link transceiver 710. Powercontrol commands 730 each designate a forward link transmit power. Inresponse to these commands, forward link transceiver 710 sets thetransmit power for the forward links controlled by the selectors 718originating these commands.

For example, selector 718 a generates a power control command 730 a thatis sent to transceiver 710 through interface 728 and router 714. Uponreceipt of power control command 730 a, forward link transceiver 710sets the power of the forward link controlled by selector 718 a. Detailsregarding this feature are described below with reference to FIG. 11.

Accordingly, each selector 718 operates with forward link transceiver710 to perform the steps described above with reference to FIGS. 5-7.For example, as described above with reference to steps 402, 404, and406, each selector 718 determines P_(baseline), P_(margin), andP_(correction).

Additionally, each selector 718 operates with forward link transceiver710 to set the corresponding P_(transmit) based on P_(baseline),P_(margin), and P_(correction). Thus, these components perform step 420.

FIG. 11 is a block diagram of a forward link transceiver 710implementation. As shown in FIG. 11, transceiver 710 includes aplurality of transceiver paths 802 a-802 n, a summer 804, and an outputinterface 805. Each transceiver path 802 receives a forward linkinformation sequence 724 and a power control command 730 from acorresponding selector 718. Although FIG. 11 only shows implementationdetails for transceiver path 802 a, transceiver paths 802 b-802 n mayinclude similar or identical features.

As shown in FIG. 11, transceiver path 802 a includes an interleaver 806,an encoder 808, and a gain module 810. Interleaver 806 receives aninformation sequence 724 and block interleaves this sequence to producean interleaved sequence 820.

Interleaved sequence 820 is sent to encoder 808, which performs errorcorrection encoding, such as turbo block encoding, to produce an encodedinformation sequence 822.

Gain module 810 receives encoded sequence 822, which is a forward linkinformation sequence. Additionally, gain module 810 receives powercontrol command 730 a from selector 718 a. Gain module 810 scalesencoded sequence 822 based on the transmit power level designated bypower control command 730 a. Thus, gain module 810 may increase ordecrease the power of encoded sequence 822. This scaling produces ascaled sequence 824.

Encoded sequence 822 is a sequence of digital symbols. This sequence maybe scaled by multiplying each of the symbols with a gain factordetermined by power control command 730. Such scaling operations may beimplemented digitally through hardware techniques, and/or softwareinstructions operating on well known elements or generalized function orgeneral purpose hardware including a variety of programmable electronicdevices, or computers that operate under the control of commands,firmware, or software instructions to perform the desired functions.Examples include a software-controlled processor, controller or device,a microprocessor, one or more digital signal processors (DSP), dedicatedfunction circuit modules, application specific integrated circuits(ASIC), and field programmable gate arrays (FPGA). Accordingly, powercontrol command 730 a may include one or more software instructionstransferred between selector 718 a and gain module 810.

As shown in FIG. 11, transceiver path 802 further includes spreadingcombiners 812 a-812 b, channelizing combiners 814 a-814 b, and aquadrature phase shift keying (QPSK) modulator 816. Spreading combiners812 a-812 b each receive scaled sequence 824 and combine (for example,multiply) this sequence with a respective PN sequence 834 to producespread sequences 828 a and 828 b.

Spread sequences 828 a and 828 b are each transferred to a respectivechannelizing combiner 814. Each channelizing combiner 814 combines (forexample, multiplies) the corresponding spread sequence 828 with achannelizing code, such as a Walsh code. As a result, combiners 814 eachproduce a channelized sequence 830. In particular, combiner 814 aproduces an in-phase (I) channelized sequence 830 a and combiner 814 bproduces a quadrature (Q) channelized sequence 830 b.

Channelized sequences 830 a and 830 b are sent to QPSK modulator 816.QPSK modulator 816 modulates these sequences to generate a modulatedwaveform 832 a. Modulated waveform 832 a is sent to summer 804. Summer804 adds modulated waveform 832 a and waveforms 832 b-832 n produced bytransceiver paths 802 b-802 n. This operation results in a combinedsignal 834, which is sent to output interface 805.

Output interface 805 up converts combined signal 834 from baseband to anIF, thereby generating forward link IF signal 722. Output interface 805may additionally perform filtering and amplification operations in thegeneration of IF signal 722.

IX. Conclusion

While various aspects have been described above, it should be understoodthat they have been presented by way of example only, and notlimitation. For example, the presently claimed invention is not limitedto satellite-based communications systems, but also may be applied toterrestrial-based systems, such as where there are multiple sectors(beams) and cross-over regions between such sectors. Furthermore, thepresently claimed invention is not limited to CDMA systems, but may beextended to other types of communications systems and air interfaces,such TDMA, FDMA, CDMA2000, WCDMA, and OFDMA systems. Moreover, while theaspects describe wireless CDMA transmission in the context of QPSKmodulation, other modulation techniques may employed.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the aspects disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the presently claimed invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a Digital SignalProcessor (DSP), an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in Random Access Memory (RAM), flashmemory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM),Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the presently claimedinvention. Various modifications to these aspects will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other aspects without departing from the spiritor scope of the claimed invention. Thus, the presently claimed inventionis not intended to be limited to the aspects shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method of controlling forward and reverse link channel transmissionpower, P_(transmit), to and from a user terminal in a wirelesscommunications system having a plurality of beams, comprising the stepsof: (a) receiving an in-use formatted message signal to noise ratio(SNR) of an active signal of interest; (b) determining a baseline powerlevel, P_(baseline), from the received active formatted message SNR,wherein the determining step comprises calculating a transmit powerlevel offset; (c) identifying an interference susceptibility of theactive signal of interest comprising the step of measuring a signalpower of at least one adjacent signal at a receiver; (d) transmitting aformatted interference message comprising segregating interferencesusceptibility into categories detected at the receiver; (e) determininga power margin, P_(margin), from the identified interferencesusceptibility; (f) identifying a quality of service metric (QSM)associated with the active signal of interest; (g) determining a powerlevel correction factor, P_(correction), based on the QSM; (h)identifying a signal fade condition associated with the active signal ofinterest; (i) determining a fade margin power level P_(fade), based onthe signal fade condition; and (j) setting P_(transmit) based onP_(baseline), P_(margin), P_(correction), and P_(fade).
 2. The method ofclaim 1 wherein the step of measuring signal power of adjacent signalscomprises measuring frequency.
 3. The method of claim 1 wherein the stepof measuring signal power of adjacent signals comprises measuringbandwidth.
 4. The method of claim 1 wherein the step of measuring signalpower of adjacent signals comprises measuring location.
 5. The method ofclaim 1 wherein the step of identifying a QSM comprises identifying amember from the group consisting of a filtered signal to noise ratio(SNR), a block error rate (BER), a symbol error rate (SER), a frameerror rate (FER) and a combination of the SNR, the BER, the FER and theSER.
 6. The method of claim 1 further comprising the step of loweringthe interference susceptibility by increasing the channel transmitpower, P_(transmit).
 7. The method of claim 1 further comprising thestep of lowering the interference susceptibility by decreasing aninterference power of the at least one adjacent signal.
 8. The method ofclaim 1 further comprising the step of adjusting a data rate andbandwidth of the active signal of interest based on a type and a powerof the at least one adjacent interfering signal.
 9. The method of claim8 wherein the formatted interference message comprises orthogonal andnon-orthogonal noise.
 10. The method of claim 8 wherein the formattedinterference message comprises a narrow band and a wide band interferer.11. The method of claim 1 wherein the step of determining a baselinepower level, P_(baseline), comprises averaging a history of the SNR ofthe active signal of interest.
 12. The method of claim 1 wherein thestep of determining a fade margin power level P_(fade), comprisesfiltering the active signal of interest SNR.
 13. A system forcontrolling forward and reverse link channel transmission power,P_(transmit), to and from a user terminal in a wireless communicationssystem having a plurality of beams, the system comprising: means forreceiving an in-use formatted message signal to noise ratio (SNR) of aan active signal of interest; means for determining a baseline powerlevel, P_(baseline), from the received active formatted message SNR,wherein the means for determining comprises a means for calculating atransmit power level offset; means for identifying an interferencesusceptibility of the active signal of interest comprising a means formeasuring a signal power of at least one adjacent signal at a receiver;means for transmitting a formatted interference message comprisingsegregating interference susceptibility into categories detected at thereceiver; means for determining a power margin, P_(margin), from theidentified interference susceptibility; means for identifying a qualityof service metric (QSM) associated with the active signal of interest;means for determining a power level correction factor, P_(correction),based on the QSM; means for identifying a signal fade conditionassociated with the active signal of interest; means for determining afade margin power level P_(fade), based on the signal fade condition;and means for setting P_(transmit) based on P_(baseline), P_(margin),P_(correction), and P_(fade).
 14. The system of claim 13 wherein themeans for measuring signal power of adjacent signals comprises a meansfor measuring frequency.
 15. The system of claim 13 wherein the meansfor measuring signal power of adjacent signals comprises a means formeasuring bandwidth.
 16. The system of claim 13 wherein the means formeasuring signal power of adjacent signals comprises a means formeasuring location.
 17. The system of claim 13 wherein the means foridentifying a QSM comprises a means for identifying a member from thegroup consisting of a filtered signal to noise ratio (SNR), a blockerror rate (BER), a symbol error rate (SER), a frame error rate (FER)and a combination of the SNR, the BER, the FER and the SER.
 18. Thesystem of claim 13 further comprising a means for lowering theinterference susceptibility by increasing the channel transmit power,P_(transmit).
 19. The system of claim 13 further comprising a means forlowering the interference susceptibility by decreasing an interferencepower of the at least one adjacent signal.
 20. The system of claim 13further comprising a means for adjusting a data rate and bandwidth ofthe active signal of interest based on a type and a power of the atleast one adjacent interfering signal.
 21. The system of claim 20wherein the formatted interference message comprises orthogonal andnon-orthogonal noise.
 22. The system of claim 20 wherein the formattedinterference message comprises a narrow band and a wide band interferer.23. The system of claim 13 wherein the means for determining a baselinepower level, P_(baseline), comprises a means for averaging a history ofthe SNR of the active signal of interest.
 24. The system of claim 13wherein the means for determining a fade margin power level, P_(fade),comprises a means for filtering the active signal of interest SNR.
 25. Acomputer program product, comprising: computer readable mediumcomprising: code for causing forward and reverse link channeltransmission power, P_(transmit), to be controlled to and from a userterminal in a wireless communications system having a plurality ofbeams, the computer code comprising: code for causing an in-useformatted message signal to noise ratio (SNR) to be received from anactive signal of interest; code for causing a baseline power level,P_(baseline), to be determined from the received active formattedmessage SNR, further comprising a calculation of a transmit power leveloffset; code for causing an interference susceptibility of the activesignal of interest be identified further comprising a measurement of asignal power of at least one adjacent signal at a receiver; code forcausing a formatted interference message be transmitted comprising asegregation of the interference susceptibility into categories detectedat the receiver; code for causing a power margin, P_(margin), bedetermined from the identified interference susceptibility; code forcausing a quality of service metric (QSM) associated with the activesignal of interest be identified; code for causing a power levelcorrection factor, P_(correction), based on the QSM be determined codefor causing a signal fade condition associated with the active signal ofinterest be identified; code for causing a fade margin power level,P_(fade), based on the signal fade condition be determined; and code forcausing a P_(transmit) be set based on P_(baseline), P_(margin),P_(correction), and P_(fade).
 26. The computer program product of claim25 wherein code for causing a measurement of signal power of adjacentsignals comprises a measurement of frequency.
 27. The computer programproduct of claim 25 wherein code for causing a measurement of signalpower of adjacent signals comprises a measurement of bandwidth.
 28. Thecomputer program product of claim 25 wherein code for causing ameasurement of signal power of adjacent signals comprises a measurementof location.
 29. The computer program product of claim 25 wherein thecode for causing a QSM be identified comprises an identification of amember from the group consisting of a filtered signal to noise ratio(SNR), a block error rate (BER), a symbol error rate (SER), a frameerror rate (FER) and a combination of the SNR, the BER, the FER and theSER.
 30. The computer program product of claim 25 further comprisingcode for causing the interference susceptibility be lowered byincreasing the channel transmit power, P_(transmit).
 31. The computerprogram product of claim 25 further comprising code for causing of theinterference susceptibility be lowered by a decrease of an interferencepower of the at least one adjacent signal.
 32. The computer programproduct of claim 25 further comprising code for causing a data rate andbandwidth of the active signal of interest be adjusted based on a typeand a power of the at least one adjacent interfering signal.
 33. Thecomputer program product of claim 32 wherein the formatted interferencemessage comprises orthogonal and non-orthogonal noise.
 34. The computerprogram product of claim 32 wherein the formatted interference messagecomprises a narrow band and a wide band interferer.
 35. The computerprogram product of claim 25 wherein the code for causing a baselinepower level, P_(baseline), be determined comprises code for causing ahistory of the SNR of the active signal of interest be averaged.
 36. Thecomputer program product of claim 25 wherein the code for causing a fademargin power level P_(fade), be determined comprises code for causingthe active signal of interest SNR be filtered.